The proceeds from the sale of bonds herein authorized, together with all special taxes and assessments to be levied for the classes of improvements designated in section 14-528, and the proceeds in the nature of all earnings and income from the investment and use thereof shall be used and employed to finance such classes of improvements, inclusive of all proper intersection charges. All such proceedings shall be credited to a fund to be designated special assessment sinking fund, and, except such part thereof as may be required to pay proper intersection charges, shall be kept and maintained within such fund. The accumulations in this fund, less the amounts thereof necessary to pay proper intersection charges from time to time, shall constitute a sinking fund to pay interest as it accrues and finally to pay at maturity all bonds issued and sold under the provisions hereof, except such part thereof as has been devoted to the payment of proper intersection charges. The proportion of bonds authorized hereunder and necessary to pay proper intersection charges, inclusive of interest thereon, shall be paid and redeemed from the general sinking fund of the city. In all cases where taxes and special assessments levied under section 14-533 have been paid and have been credited to the special assessment sinking fund, such taxes and special assessments as well as all other credits in said fund may be used to finance other improvements, but only to the extent which will leave the fund available to pay all bonds issued to finance street improvements and interest thereon when maturing or due, except such part as by this section is charged to the general sinking fund of the city.